Field of the Invention
The present invention relates to the field of enzyme engineering, which relates to a mutant with enhanced secretion of L-asparaginase and its application.
Description of the Related Art
L-asparaginase (EC3.5.1.1) is an enzyme used effectively in the treatment of cancer. It catalyzes the hydrolysis of amino acid L-asparagine to aspartic acid and ammonia. L-asparaginase has been proved to have inhibitive activity on tumor cells, especially on acute leukemia and malignant lymphoma. Besides the cancer-combating properties and no inhibitory on bone marrow cells, L-asparaginase is employed as effective drugs in the treatment of acute lymphoblastic leukemia (ALL).
Two forms of L-asparaginases have been reported, namely L-asparaginase I and L-asparaginase II. The properties of these two enzymes, especially enzymes from Escherichia coli, Erwinia carotovora, and Erwinia chrysanthemi, have been studied intensively. Since it has been proved that only L-asparaginase II has cancer-combating properties, most research is about L-asparaginase II. L-asparaginase II produced by Escherichia coli and Erwinia chrysanthemi has already been developed into drugs for acute lymphoblastic leukemia treatment.
Acrylamide is formed through Maillard reaction which happens when sugars and asparagine are heated under high temperature. L-asparaginase can reduce the content of acrylamide in food.
L-asparaginase has been widely found in microbials, mammals and plants. Compared with the low content of L-asparaginase in animal serum, and the complex extraction process, there are advantages of L-asparaginase produced by means of microorganism fermentation, including easy cultivation and low costs. Current L-asparaginase is mainly produced by microorganisms including Escherichia coli, Erwinia carotovora, Erwinia chrysanthemi, etc. However L-asparaginase shows low yield in wild strains. In recent years, high efficient expression of L-asparaginase has become an important source for L-asparaginase production, which is realized by Escherichia coli expressed L-asparaginase gene.
However, the critical problem to be solved is to realize L-asparaginase expression in food safety strains and improve its secretion.